1. Field of Invention
This invention generally concerns an expansion chuck for the working spindle of a machine tool, and more particularly such a chuck having a rigid chuck body with a central receptacle bore for the shaft to be chucked, an elongated toroidal chamber which is coaxial with the receptacle bore in the one-piece chuck body and is filled with an incompressible fluid, as well as a device for generating a hydraulic pressure in said toroidal chamber.
2. Discussion of Related Art
Expansion chucks of the type of interest here are known in various embodiments and are mostly used for accurately centered chucking of a tool shaft such as the shaft of a drill or a milling cutter to secure these tools in the working spindle of a corresponding machine tool. With these types of hydraulic expansion chucks, which are known from German Utility Model 9,411,260, or from unexamined German Patent 2,700,934, for example, the toroidal chamber formed in the body of the chuck is bordered on the inside radially by a so-called expansion sleeve which undergoes elastic deformation radially toward the inside when hydraulic pressure is applied in this toroidal chamber, thereby securely gripping on all sides the tool shaft inserted into the receptacle bore.
A Tendo brochure from Fritz Schunk GmbH describes a hydraulic expansion chuck for tool sharpening and grinding machines, where the toroidal chamber filled with the incompressible liquid is deformed in the cylindrical chucking part of the chuck body, where the radial inside wall of this toroidal chamber has a relatively small wall thickness and undergoes deformation radially toward the inside under the hydraulic pressure in the toroidal chamber to chuck the tool shaft. After the central receptacle bore for the tool shaft there is a threaded bolt in a cross hole having a polygonal opening on its end which is accessible from the outside for insertion of a tool and having an outside thread in this enlarged end head which engages with an inside thread worked into part of this cross hole. At the other end of the shaft of this bolt, there is a piston which is moved back and forth by a screw action of the bolt in a cylindrical space with a sealing effect. This cylindrical space communicates with the toroidal chamber through an axially parallel channel in the body part of the chuck. By turning the bolt using a tool inserted from the outside, the internal pressure in the toroidal chamber necessary for the chucking operation and for the elastic deformation of the inside wall is created by means of the corresponding piston displacement in the cylinder filled with incompressible liquid. However, this expansion chuck as well as others that are already known were designed only for chucking a one-piece part such as the shaft of a tool.
On the other hand, so-called expansion mandrels for centrally securing hollow cylindrical work pieces for lathing, for example, are already known, where a narrow toroidal chamber which determines the respective chucking range is formed in a corresponding recess in the body of the mandrel which is limited toward the outside radially by an expansion sleeve. This external expansion sleeve is expanded radially outward, thus chucking the work piece placed previously on the mandrel, due to the buildup of an internal hydraulic pressure in this toroidal chamber filled with incompressible liquid.
German Patent 743,530 describes a chucking device for machine tools having a double-walled chucking sleeve for securing a hollow cylindrical tool on a shaft. The chucking sleeve is designed with a double wall and is securely attached to one end with a toroidal rotating body which accommodates a device for producing a hydraulic pressure in the elongated toroidal chamber of the chucking sleeve. Due to this hydraulic pressure in the toroidal chamber, the two peripheral walls of the double-walled chucking sleeve undergo elastic deformation with a radial inward and radial outward force, and are brought into pressure contact with the outside surface of the shaft and with the inside surface of the hollow cylindrical tool. Simultaneous chucking of two tools is neither provided here nor is it readily feasible.
International patent publication WO 93/18880 describes a hydraulic work holding bushing for chucking lathe tools in the tool receptacles of a revolver head having a thin-walled hollow cylindrical chucking part and a ring body connected to it. An elongated toroidal chamber communicates with a device arranged in the ring body to generate an internal hydraulic pressure. The two peripheral walls of the toroidal chamber are thin and undergo elastic deformation due to the hydraulic pressure in the toroidal chamber, so they are brought into pressure contact with the outside wall of the lathe tool and against the inside wall of the tool receptacle.
Finally, it is known from German Patent 1,552,257 and German Utility Model 9,411,260 that the shaft of a tool can be chucked in an expansion sleeve positioned separately in the chuck and additionally secured by teeth or by claw engagement, for example, to prevent twisting.